What is optical interferometry?
According
to Hajian and Armstrong, the central concept at work in interferometer
technology is the combination of two nearly identical signals to produce
interference, thereby yielding information not given by either signal
individually. In optical
interferometry, the combination of light waves upon entering the interferometer
is controlled by carefully positioned primary mirrors within the
instrument. Because light from a
distant star often hits one of the primary mirrors before the other, there are
delay lines, or adjustable mirrors on slides along the respective light paths
that can be positioned to ensure that both beams of light reach a common
detector at the same time. When
constructive and destructive interference occurs between the two beams of
light, a pattern of high and low intensity bands, or fringes, is formed. An infinitesimally small source will produce
interference fringes that have a high contrast, whereas larger sources will
produce fringes with reduced contrast.
Using sophisticated Fourier transform algorithms, astronomers can
examine the contrast and visibility of the fringes to map the celestial body
being observed.
Optical
interferometers are used primarily for the measurement of the angular diameters
of stars and binary star orbits. The resolution obtained by an interferometer depends on the
interferometer’s baseline, the distance between its component telescopes,
rather than on aperture size as is true with common telescopes. Many recent interferometers have several
mirrors in their arrays, and therefore have many different baselines. Astronomers often employ the natural
rotation of the earth to take measurements from several baselines consecutively.
The Basic Elements of an Optical
Interferometer
http://www.sciam.com/2001/0301issue/0301armstrong.html
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